Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
Sensei - Create and sell online courses with Sensei LMS plugin for WordPress - engaging lessons, interactive quizzes, and simple student management.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Web Uptime - Multi-location website uptime monitoring
Better Uptime - We call you when your website goes down
Platypus - Realtime server monitoring and reporting